Motor vehicles having a drive unit, a driven end, and a transmission connected between the drive unit and the driven end have been known from practical experience for a long time. The operation of the drive unit is controlled by an engine control unit by an open-loop system and/or a closed-loop system. The operation of the transmission is controlled by a transmission control unit by an open-loop system and/or a closed-loop system.
A transmission is a gearbox having multiple shift elements. The shift elements are friction-locking shift elements, such as clutches and brakes, or are form-fit shift elements, such as shifting dogs. In order to implement a gear shift or a gear change in a gearbox, at least one previously engaged shift element is disengaged and at least one previously disengaged shift element is engaged in order to transfer the transmission from an actual gear into a target gear. In particular, for the case in which a form-fit shift element is the shift element to be engaged and, therefore connected, contributes to the implementation of a gear shift, the form-fit shift element must first be synchronized via an engagement of the drive unit. The shift element to be engaged is engageable only after an appropriate synchronization. Torque cannot be transmitted by the transmission during this time. In particular, for a downshift to be implemented originating from a coasting condition of the motor vehicle, the absence of the thrust torque at the driven end is perceived as unpleasant by the driver, since the braking effect of the drive unit is missing during the gear shift. For the case in which the driver intentionally initiates a downshift during downhill travel, for example, in an inching operation, the omission of the thrust torque from the drive unit at the driven end is perceived as particularly disadvantageous. The same applies for hybrid vehicles, in which, in the coasting condition, the thrust torque utilized for recuperation is relatively high.
There is a need, therefore, for a method for operating a motor vehicle, and for a transmission control unit, that allows downshifts to be implemented more comfortably originating from a coasting condition of the motor vehicle.